Diastereoselective Ring Expansion Rearrangements of (Benzocyclobutenone)‐and (Benzocyclobutenedione)chromium Complexes: Syntheses of Substituted 1‐Indanone and 1,3‐Indandione Complexes

Organolithium and Grignard reagents add to the oxo group of (benzocyclobutenone)tricarbonylchromium(0) ( 1 ) diastereoselectively from the exo face of the organic ligand. If acyl anion equivalents are used as nucleophiles, deprotection of the carbonyl functions of the adducts causes ring expansion reactions to occur. Among these a rare example of an anion‐accelerated 1‐vinylcyclobutenol–cyclohexadienol rearrangement is reported which results, after isomerization, in a naphthol complex. Other ring expansion reactions gave coordinated substituted indanone derivatives. The facial differentiation by the tricarbonylchromium moiety allows for the first time the determination of the distereoselectivity of these reactions. The 1‐oxoindan‐2‐ol derivatives obtained can undergo an α‐ketol rearrangement with formation of the corresponding 2‐oxoindan‐1‐ol complexes. Some of these reactions were performed with nonracemic starting material in order to determine how far chirality transfer from the planar chiral starting material to C‐2 in the indanone system was possible. The ring expansion was also feasible with the benzocyclobutenedione complex as a starting compound, the reaction giving substituted 1,3‐indandione complexes. Crystal structure analyses of three of the complexes prepared are reported.